The present invention relates to electron-beam evaporation systems, especially electron-beam evaporation systems for use with rod materials that sublimate when heated with an electron beam at low pressures.
Electron-beam evaporation systems direct an electron beam to an ingot material to evaporate this material and coat a substrate. A discussion of electron-beam technology is given in the book Physical Vapor Deposition, R. Hill, ed., 1986, Second Edition, at pages 17-106, which is incorporated herein by reference. FIG. 1 is a diagram illustrating a prior art electron-beam evaporation system adapted from page 64 of Physical Vapor Deposition. The system 10 includes an electron beam source 12 which supplies an electron beam 14 to contact an ingot material positioned in the crucible 16. The evaporated ingot material is deposited on the substrate 18 in the process chamber 20.
FIG. 2 is a diagram of a prior art system adapted from page 39 of Physical Vapor Deposition. This reference uses feed stock 24 contacting a water-cooled crucible 26. As the material of the feed stock evaporates, the feed stock can be pushed upward to provide a continuous supply of the feed stock. In this diagram, the feed stock is not a subliming material, so a liquid inventory 24a is formed. The electron beam source 28 includes a cathode block 28a, a filament 28b, and anodes 28c. Permanent magnets cause the 270.degree. deflection of the electron beam 30 so that the electron beam 30 contacts the material of the rod 24.
It is also possible to use subliming materials that do not produce a liquid inventory 24a. Subliming materials have the problem that, since no liquid inventory is formed, hot spots on the ingot surface can occur. The electron beam may drill into the ingot material at the hot spot so that the erosion from the ingot surface is not even. This can require the ingot to be replaced when only a small percentage of the ingot was used. In order to avoid some of these problems, sweep mechanisms are used. One type of sweep mechanism is called X-Y sweep, because it varies the longitudinal and lateral positioning of the beam with a variable amplitude and frequency for each axis. This enables the electron beam spot to be swept more uniformly over a wide range of source sizes. The X-Y sweep is used in conjunction with a continuous rod rotation and feed. A Temescal Model SRIHS-270-2 rod-fed electron gun uses such a rod feed and rotation mechanism, as well as an X-Y sweep mechanism.
A disadvantage of prior art rotational rod-fed systems is that it is difficult to maintain a uniform power density and thus evaporation rate off of the rod tip. It is desired to have an improved electron-beam evaporation system.